Homebrew Decompiler is a GPLed tool (written in C++) that takes Java .class files and reverse engineers the JVM bytecodes to generate .java files that attempt to resemble the original source code as much as possible.

spim is a self-contained software simulator for running R2000/R3000 assembly language programs. It reads and can immediately execute files containing assembly language code. spim also provides a debugger and simple set of operating system services. spim provides both a simple, textual interface and a fancier, graphical interface. The package includes complete source code and documentation.

revava is a single-pass disassembler that reads in a file
containing a program intended for an Atmel AVR microcontroller,
and outputs assembly code that can be input to an AVR
assembler. The output of revava contains assembler mnemonics
where possible and dc.W declarations where no mnemonic matches
the data. The comment field for each assembly instruction
contains the address from the object code and the destination
address for branches, calls, jumps, etc. In the case where
there are multiple assembly instructions that assemble to the
same opcode, all choices are presented in a group with all but
the first choice commented out.

The bastard disassembler is a disassembler written for x86 ELF targets on
Linux. Other file formats/CPUs can be 'plugged in'. It has a command-line
interface and is meant to be used as a backend or engine. Support for
controlling the disassembler via pipes is provided. Note that this
disassembler does not rely on libopcodes to do its disassembly. Rather, the
'libi386' plugin is a standard .so that can be reused by other projects.

jclasslib bytecode viewer is a tool that visualizes all aspects of compiled Java class files and the contained bytecode. In addition, it contains a library that enables developers to read, modify, and write Java class files and bytecode.

ps2tiffs extracts the sampled images from a
PostScript document. It is not a PostScript
renderer. ps2tiffs is a system where the grazer
feeds on the output of a PostScript interpreter
whose image operators have been replaced by
special data-hijacking functions. This has the
benefit of allowing the extraction of images
regardless of how they have been encoded,
formatted, scaled, or squished by the app which
generated the PostScript document. It outputs
greyscale, RGB, and CMYK TIFFs.

OpenMCL is an Open Source version of Digitool's excellent Macintosh Common Lisp (MCL) implementation, which runs on LinuxPPC and MacOS X. It features a native code compiler, multithreading support, and good ANSI CL compliance.